Graded drilling cutter

ABSTRACT

In an embodiment, an abrasive compact includes ultra-hard particles which are sintered, bonded, or otherwise consolidated into a solid body. The compact also includes various physical characteristics having a continuous gradient, a multiaxial gradient, or multiple independent gradients.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/886,711, filed on Jan. 26, 2007.

Not Applicable

BACKGROUND

1. Technical Field

This application relates to abrasive compacts with various physicalcharacteristics, such as compacts having a continuous gradient, amultiaxial gradient, or multiple independent gradients.

2. Description of the Related Art

Abrasive compacts are widely used in drilling, boring, cutting, milling,grinding and other material removal operations. Abrasive compactsinclude ultra-hard particles sintered, bonded, or otherwise consolidatedinto a solid body. Ultra-hard particles may include natural or syntheticdiamond, cubic boron nitride (CBN), carbo-nitride (CN) compounds,boron-carbon-nitrogen-oxygen (BCNO) compounds, or any material withhardness greater than that of boron carbide. The ultra-hard particlesmay be single crystals, polycrystalline aggregates or both.

In commerce, abrasive compacts are sometimes referred to aspolycrystalline diamond (PCD), or diamond compacts when based ondiamond. Abrasive compacts based on CBN are often called polycrystallinecubic boron nitride (PCBN) or CBN compacts. Abrasive compacts from whichresidual sintering catalysts have been partially or totally removed aresometimes called leached or thermally stable compacts. Abrasive compactsintegrated with cemented carbide or other substrates are sometimescalled supported compacts.

Abrasive compacts are useful for demanding applications requiringresistance to abrasion, corrosion, thermal stress, impact resistance,and strength. Design compromises for these abrasive compacts arise fromthe difficulty of attaching the abrasive compact to supportingsubstrates, sintering process limitations, or balancing inverselyvarying properties, such as the need for sintering additives an theireffect on corrosion resistance. Prior art abrasive compacts use layeredmicrostructures to overcome some of these design compromises. The priorart's transition between layers with different ultra-hard particle sizesis shown in FIG. 1, where a uniform fine particle region 111, with fineparticles 114 and uniformly coarse region 112 and respectively 113, arevisible. FIG. 2 shows the abrupt change in particle size of the compactof FIG. 1 that appears 550 microns from the active cutting surface ofthe cutter.

Prior art compacts also use abrupt chemical transitions. FIG. 3, anelectron micrograph, illustrates a catalyst concentration change 213,214 in a prior art supported abrasive compact. The catalyst metaldepleted region 211 is near the active cutting surface 217. The catalystmetal is visible in the metal rich region 212 as a fine network of lightgray lines. The transition also may be shown by electron beam microprobeanalysis conducted along the line heading from one surface 215 toanother 216. FIG. 4 graphically illustrates the five-fold reduction incatalyst concentration of the cutter of FIG. 3 along the line betweensurfaces 215 and 216. Both transitions take place over about one coarsegrain diameter.

The abrupt transitions in physical properties or structure of prior artabrasive compacts are also supported by patent drawings of, for example,U.S. Pat. No. 5,135,061, U.S. Pat. No. 6,187,068, and U.S. Pat. No.4,604,106, the disclosures of which are incorporated herein by referencein their entirety. The foregoing abrasive compacts all contain discretelayers of essentially uniform physical characteristics with abrupttransitions between the regions. Abrupt transitions in physical,chemical or structural characteristics can reduce performance ofabrasive compacts.

SUMMARY

In an embodiment, an abrasive compact includes a plurality ofsuperabrasive particles consolidated into a solid mass. The particleshave a characteristic gradient that is continuous, monotonic anduniaxial.

Optionally, the characteristic gradient is a particle size gradient.Additionally, the maximum rate of change of particle size along an axismay be less than 1 micron of diameter per 1 micron of translation.

Alternatively, the characteristic gradient may be a pore size gradient.Additionally, the maximum rate of change of pore size along an axis maybe less than 1 micron of diameter per 1 micron of translation.

As another option, the characteristic gradient may be a particle shapegradient. Additionally, the maximum rate of change of particle aspectratio along an axis may be less than 0.1 per 1 micron of translation.

In yet another option, the characteristic gradient may be asuperabrasive particle concentration.

In another embodiment, an abrasive compact includes superabrasivematerial consolidated into a solid mass. This mass has at least twocharacteristic gradients that are each continuous. The gradients may be(i) monotonic and uniaxial or (ii) oscillating.

In an embodiment, a method of creating an abrasive compact includesstarting with a group of ultra-hard particles, such as a preparedsynthetic diamonds, with a range of particle sizes. The particles arecombined and mixed with alcohol or another fluid to create a mixedslurry. The slurry is allowed to settle or otherwise separate. The mixedslurry settles into a substantially solid, graded layer, optionally inwhich more of the coarse particles have first settled and more of thefinest particles have settled last. Most, if not all, remaining liquidis removed by drying, centrifugation, or another method. A portion ofthe graded layer is then removed and processed by sintering, typicallyunder HPHT conditions, to create an abrasive compact. A portion of thegraded layer optionally may be placed against a substrate. The layer ofultra-hard particles may be oriented in order to place the surfacehaving more coarse diamond particles near the substrate to create aninitial assembly, which is processed by sintering, typically under HPHTconditions, to create a processed assembly. From this processedassembly, a sintered diamond abrasive compact supported on a cobaltcemented tungsten substrate is produced and recovered. The resultingsupported sintered compact may be finished into an abrasive tool.

Optionally, the mixed slurry is allowed to separate in a non-planarfixture. Additionally, the substrate may have an interface surfacematching the graded layer, and it may be placed against the portion ofthe compact having more fine particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electron micrograph of a prior art PCD compact structure,illustrating an abrupt transition and particle size.

FIG. 2 is a graph showing particle size transition as a function ofdistance from cutting surface, which is relevant to the cutter of FIG.1.

FIG. 3 is an electron micrograph illustrating an abrupt catalystconcentration change in a prior art thermally stable supported abrasivecomposite.

FIG. 4 is a graph of cobalt catalyst concentration as a function of thedistance from the cutter interface, which is relevant to the cutter ofFIG. 3.

FIG. 3 is a block diagram from the prior art illustrating various layersof a superabrasive cutter.

FIG. 4 is a diagram of a prior art cutter having particles of differentsizes arranged in circumferential regions.

FIG. 5 is a diagram illustrating a cross section of an exemplarycylindrical supported abrasive composite.

FIG. 6 is an electron micrograph illustrating an exemplarymicrostructure of an embodiment such as that of FIG. 5.

FIG. 7 is a graph comparing grain size as a function of distance fromthe cutting surface for the embodiments of FIG. 3 and FIG. 5.

FIG. 8 includes electron micrographs of an exemplary cutter havingmultiple independent gradients, including high magnification insets.

FIG. 9 is a graph illustrating grain size as a function of the distancefrom the active cutting surface, based on the embodiment of FIG. 8.

FIG. 10 is a graph showing tungsten content, catalyst metalconcentration, and particle size gradients in an exemplary cutter.

FIG. 11 is a schematic section of a supported abrasive compact withmultimodal gradients present on multiple axes.

FIG. 12 is a micrograph of a gradient from a region of the cutter ofFIG. 11.

FIG. 13 is a graph of a particle size gradient, while FIG. 14 showscatalyst metal concentration, in one direction for the exemplary cutterof FIG. 12.

FIGS. 15 and 16 show catalyst metal concentration and particle sizegradients of the exemplary cutter of FIG. 12 in a direction that isdifferent from that shown in FIGS. 13 and 14.

FIG. 17 is a graph showing particle size distribution of the exemplarycutter of Example 3 presented herein.

FIG. 18 is a graph illustrating particle size distributions of thediamond powder used in Example 4.

FIG. 19 is a graph illustrating particle size distributions of thetungsten powder used in Example 5.

FIG. 20 illustrates a compact and an exemplary settling fixture.

DETAILED DESCRIPTION

Before the present methods, systems and materials are described, it isto be understood that this disclosure is not limited to the particularmethodologies, systems and materials described, as these may vary. It isalso to be understood that the terminology used in the description isfor the purpose of describing the particular versions or embodimentsonly, and is not intended to limit the scope. For example, as usedherein, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. In addition,the word “comprising” as used herein is intended to mean “including butnot limited to.” Unless defined otherwise, all technical and scientificterms used herein have the same meanings as commonly understood by oneof ordinary skill in the art.

This disclosure deals with solid materials in which at least onecharacteristic, such as structure or another physical characteristicsvaries with position in the material. As used herein, the followingterms have the following definitions:

Areal Average—an average of a measured characteristic assessed in asection of a compact oriented with respect to the gradient axis. Thedimension perpendicular to the gradient axis is large enough give a goodestimate of the characteristic, at least 30 coarse particle diameters,and in some cases 100 or more. The dimension parallel to the gradientshould be small enough not to obscure the presence of discontinuities,such as at least 1 to 3 times the diameter of the coarsest particle inthe section of interest.

Coarse Grain—The grain of a polycrystalline compact having the 99^(th)(largest) percentile diameter of those grains present in a sample areaof a compact.

Concomitant Gradients—multiple structural or physical characteristicsthat simultaneously vary as a function of position, or structural orphysical characteristics that simultaneously vary along one or multipleaxes of an object. A causal relationship exists between the gradients.

Continuous Gradient—a smooth gradient without abrupt transitions at themicrostructural scale of the compact. A continuous gradient, describedmathematically, may have a finite first positional derivative.

Continuous Characteristic Gradient—a characteristic that varies as afunction of position at about or below the scale of the microstructureof the compact. A continuous characteristic exhibits a smooth positionaldependence of the average of at least 30 randomly selected, differentline intercept assessments of the characteristic along the gradientaxis. Alternatively, a continuous characteristic gradient exhibits asmooth positional dependence of an areal average of the characteristicwhen the smaller dimension of the assessment area is oriented parallelto the gradient axis.

Continuous Variable—a variable in which changes occur in smallincrements such that large swings do not occur in a relatively smallportion of the change.

Gradient—a change in a structural or physical property based on positionwithin a solid body. The definition encompasses structure and/orphysical characteristic changes. A gradient is sometimes referred toherein as a “characteristic gradient,” where the characteristic is thestructural or physical property that changes.

Linear Gradient—a gradient in which particle size, chemical composition,or both change as a linear function of position.

Monotonic Gradient—a gradient in which a characteristic continuallyincreases or decreases with position and does not oscillate.

Multiaxial Gradient—a gradient that varies along more than one axis.

Multimodal Gradient—more than one independent structural or physicalcharacteristic gradients. The gradients may or may not have a casualrelationship with each other. As a non-limiting example, a compact inwhich both ultra-hard particle size and composition simultaneously varyhas a multimodal gradient.

Oscillating Gradient—a continuous gradient in which a characteristicrepeatedly varies between limiting values as a function of position.

Ultra-hard Material—diamond, cubic boron nitride, or another materialhaving a Vickers hardness of greater than about 3000 kg/mm², andoptionally more than about 3200 kg/mm². Ultra-hard material is sometimesreferred to herein as superabrasive material.

Uniaxial Gradient—a gradient along a single directional axis.

Unimodal Gradient—a gradient of a single structural or physicalcharacteristic. As a non-limiting example, increasing ultra-hardparticle diameter along a direction in an abrasive compact provides aunimodal gradient. Concomitant gradients along multiple axes of anobject may be associated with a unimodal gradient.

In accordance with embodiments disclosed herein, an abrasive compactincludes diamond, cubic boron nitride (CBN) or other particles ofultra-hard material consolidated into a solid mass. Any now or hereafterknown consolidation method may be used to create the mass, such assintering at elevated temperatures and pressures known as highpressure/high temperature (HPHT) conditions. For polycrystalline diamond(PCD) or polycrystalline CBN (PCBN), these conditions are typically over4 gigapascal (Gpa) and temperatures over 1200° C. The abrasive compactsmay be free standing, attached to a substrate to form a supportedabrasive compact, and/or processed to form a thermally stable, orleached, abrasive compact.

In one form, an abrasive compact may have at least one continuousuniaxial characteristic gradient of a continuously distributedstructural or physical characteristic. FIG. 5 is a schematic crosssection of a cylindrical supported abrasive composite such as the typethat may be used as a drilling cutter in an earth-boring bit. Thesection shown is parallel to the cylindrical axis 850 of the drillingcutter. Such cutters comprise a substrate 820 made of a supportingmaterial such as cemented tungsten carbide, with a compact 810 ofsintered ultra-hard particles coaxially attached to at least one end ofthe substrate. The free planar end 830 of the abrasive compact and aportion of the cylindrical abrasive compact side surface 831 are activecutting surfaces.

In embodiments described herein, the abrasive compact microstructure hasa continuous size gradient of ultra-hard materials, typically in theform of particles. The gradient shown in FIG. 5 is substantiallyparallel to the cutter cylindrical axis 850. However, other positionalgradients are possible, such as a gradient that extends inward from acorner 816 of the compact along a line that is offset at desired anglesfrom top surface 830 and side surface 831. The illustrated unimodal,uniaxial gradient in ultra-hard particle size is an independentcontinuous characteristic gradient. A relatively high concentration offine ultra-hard particles 813 provides high abrasive wear and fractureresistance near the cutting surface, while a relatively highconcentration of coarser particles 814 will be present near the tungstencarbide substrate 820. The region of fine particles 811 may extend someaxial distance toward the substrate 820 to encompass the entire activecutting surfaces 830 and 831. The linear or areal average particle size,measured as described above, smoothly and continuously increases axiallytoward the substrate 820.

The micrograph of FIG. 6 shows one microstructure of an embodiment suchas that schematically illustrated in FIG. 5. Ultra-hard particle sizes910 are measured and recorded on micrograph. The active cutting surfaces930 and 931 comprise ultra-hard particles that, in this example, arebetween about 6 and 8 microns in size for high abrasion resistance.Particles of other sizes may be used. The ultra-hard particle sizecontinuously increases to about 40 microns in the direction toward thesubstrate interface 940. The ultra-hard particle size characteristicchanges in a continuous gradient, and thus is distinctly different fromprior art layered and discontinuous mixture gradients. In someembodiments, the maximum rate of change of the particle size gradientmay be no more than 1 micron of particle size per 1 micron oftranslation (i.e., physical distance) along the gradient axis. Analternative gradient may be pore size, with a similar maximum rate ofchange.

FIG. 7 compares graphical presentations of the ultra-hard particle sizetransitions in prior art compacts 1001 (such as that shown in FIG. 3)and the embodiment of FIGS. 5 and 6 1002. The ultra-hard particle sizesare measured in a direction parallel to the cylindrical axis of thedrilling cutter (axis 850 in FIG. 5). FIG. 7 shows a continuous gradient1002 in ultra-hard particle size for the embodiment of FIG. 5, in clearcontrast with the abrupt particle size transition 1001 of the prior artof FIG. 3. While the embodiment of FIG. 5 has a nominally lineargradient 1002 in particle size, a linear gradient is not required, norshould it limit the scope of the invention. This compact also may haveseveral concomitant gradients: (i) a concomitant continuous, uniaxialgradient in wear resistance, a continuous variable; (ii) a concomitant,continuous, uniaxial composition gradient, a discontinuous variable; and(iii) others, such as catalyst metal pool size, thermal conductivity,and/or thermal expansion. The gradients described herein may encompass aportion of the abrasive compact volume as shown or the entire volume.The abrasive compacts described herein may achieve the objectives ofprior art without the stress concentration or contamination of discreteinterfaces of a layered structure. The abrasive compacts describedherein are the first reduction to practice of a continuous, uniaxialgradient of a continuously distributed compact variable.

Another embodiment is an abrasive compact with multimodal gradients.These independent gradients may be continuous or not, and they mayinclude continuously or discontinuously distributed structural orphysical characteristics. The gradients may be monotonic or oscillating.As an example, an abrasive compact may contain independent gradients ofcontinuously distributed sizes of ultra-hard particles and additiveparticles and discontinuously distributed composition characteristics.

In such an embodiment, an example of which is shown in FIG. 8, amicrograph of a sectioned drilling cutter, illustrates an abrasivecomposite with multiple independent coaxial gradients, comprising asubstrate 1120 of a tungsten carbide and/or other material with anabrasive compact 1110 of diamond and tungsten carbide and/or othermaterial coaxially attached to the substrate. The free planar end 1130of the abrasive compact and a proximal portion 1135 of the cylindricalabrasive compact surface are active cutting surfaces. As shown in thehigh magnification inset, 1115, fine ultra-hard particles 1113, in thisexample having a particle size below about 3 microns, comprise theactive cutting surfaces, providing high abrasive wear and fractureresistance while coarser particles, shown in high magnification inset1116, in this example having a particle size above about 20 microns 1114improve HPHT sintering near the tungsten carbide substrate 1120. Theregion of fine ultra-hard particles extends some axial distance towardthe tungsten carbide substrate 1120 to encompass an extended portion ofactive cutting surfaces 1135. The characteristic particle size gradientbegins at about 3 microns average particle size and continuouslyincreases axially from the free planar end 1130 toward the direction ofthe substrate 1120, achieving a final particle diameter of about 20microns. FIG. 9 presents a graph illustrating the diamond size gradient1220 as a function of distance from the free planar end and/or activecutting surface.

The second gradient set of this embodiment, independent from and coaxialwith the previously described ultra hard particle size gradientcomprises gradients in the characteristics of an additive, tungstencarbide. The tungsten carbide additive has both a particle size andmixture compositional gradient. As shown in the insets A and B of FIG. 8and in the graph of FIG. 9, the average tungsten carbide particle sizegradient 1210 continuously decreases from about 15 microns 1114 near thetungsten carbide substrate 1120 to nearly 0 microns 1113, meaning verylittle tungsten carbide is present, at the active cutting surface 1130.The continuous tungsten carbide composition gradient, coaxial withultra-hard particle size gradient, decreases from about 50 weightpercent near the tungsten carbide substrate 1120 to approximately 0% atthe planar end and/or active cutting surface 1130.

FIG. 10, an elemental concentration microanalysis, shows the independentnature of these gradients in arbitrary composition units. The tungstencarbide, measured as elemental tungsten, content 1310 of the abrasivecompact decreases in an axial direction moving away from the tungstencarbide substrate. An independent ultra-hard particle size gradient 1320also may show a decrease with distance from the substrate, while thecobalt catalyst metal concentration 1320 may increase in the samedirection. As in the prior embodiment, other concomitant gradients, suchas cobalt particle size or diamond concentration, may be present. Theindependent gradients may encompass a portion or the complete volume ofthe abrasive compact. The multimodal gradients may provide additionalcompact design flexibility while reducing the contamination and stressconcentration of the prior art.

Yet another embodiment comprises independent continuous gradients onmultiple axes within the abrasive compact. These gradients may be of anytype previously mentioned. FIG. 11 is a schematic section of a supportedabrasive compact 1400 with multimodal gradients present on multipleaxes. The schematic section intersects the cylindrical axis 1450 of thecompact. A radial direction is also shown 1460. The exterior of theabrasive compact comprises a planar active cutting surface 1410 and acircumferential surface 1411, a portion of which may be an activecutting surface. Ultra-hard particles, which may in embodiments rangefrom fine 1431 to coarse 1432 are present in the abrasive compact. Asecond gradient, such as a composition gradient, a property, or othergradient 1440 is present in the abrasive compact. This second gradientcharacteristic is illustrated by changing shade. Non-planar features1470 may be present at the interface of the supporting substrate 1420and the abrasive compact 1400. In this non-limiting example it is seenthat particles of essentially one size are present at the exteriorsurface of the abrasive compact. Note that the particles need not beexactly the same size hut merely need to be closely similar in size,such as by a 10 percent or less variation, a 5 percent or lessvariation, or a one percent or less variation. Particles of a differentsize may be present at the interior. The particles may change average ormean size on more than one axis and the rate of particle size change mayvary on different axes, such as axial 1450, radial 1460 or otherdirections. Other characteristic gradients may include concomitantgradients in catalyst metal concentration; catalyst metal distribution;ultra-hard particle concentration the amount or fraction of the compactthat is porous, known as pore fraction; the size of the pores present inthe compact, known as pore size; and shape distributions and derivativegradients in other physical characteristics. The second gradient 1440may be a gradient of any of the types mentioned above, for example agradient in the concentration or particle size of an additional phase.The multiple gradients may be oscillating, monotonic, linear or of othertypes.

FIG. 12 is a micrograph of an actual multiaxial, multimodal gradientfrom the region 1470 of FIG. 11. The direction parallel to the cuttercylindrical axis 1550 and the radial direction 1560 are indicated. Thesupporting substrate 1520, coarse ultra-hard abrasive grains 1532 andfine ultra-hard abrasive grains 1531 are shown. Radial and axialultra-hard particle size gradients are present. The rate of change ofthe particle size also varies with the axis chosen.

FIG. 13 shows the smooth axial gradient 1570 in ultra-hard particle sizefrom about 5 microns near the exterior of the compact to about 35microns near the carbide substrate 1520. FIG. 14 shows the catalystmetal concentration gradient 1580 in the same direction as assessed by asingle line scan. The variability in the catalyst concentration, duemuch lower level of catalyst present in the abrasive particles, does notobscure the presence of the gradient. The variability may be reduced byaveraging a statistically significant number of line scans parallel tothe gradient or areal assessment as described previously. FIGS. 15 and16 show the same physical characteristic gradients in the radialdirection. A lower rate of change is present in the radial direction.Multiaxial gradients further enhance design flexibility.

One form of multiaxial gradients may be found in an abrasive compactwhere an entire surface or volume, for example the entire exteriorsurface, has at least one substantially uniform physical characteristic,while having gradients in other regions. As an example, this embodimentmay include a supported abrasive composite for an earth boring bitcutter having a uniform ultra-hard particle size on all exteriorsurfaces with interior gradients to improve sintering or managestresses. In such an embodiment, concomitant gradients may be present.This embodiment may further improve design flexibility while eliminatingundesirable preferential wear during cutter service.

In another embodiment, the several structural or physicalcharacteristics may vary in some, but not all directions. For example, acontinuous axial composition gradient may coexist with a radialultra-hard particle size gradient. In such an embodiment, concomitantgradients may be present.

In still another form, the compacts described herein may exhibit adiscontinuous gradient of other phases mixed with ultra-hard particles.In one example, cutting tools for machining reactive metals requiresupported abrasive compacts with active cutting surfaces unreactivetoward the workpiece and simultaneous high reactivity toward thesubstrate. Additions of aluminum oxide in the abrasive composite canadvantageously reduce the cutting surface reactivity, but may alsodisadvantageously reduce the interfacial bond strength between theabrasive composite and a tungsten carbide substrate. The abrasivecompacts of various embodiments may have an aluminum oxide rich activecutting surface that continuously changes to a lower aluminum oxideconcentration composition at the substrate interface. In this way, acutting tool may have improved life, little or no undesirable abrupttransitions, and strong attachment to a tungsten carbide substrate.

One other embodiment incorporates particle shape gradients. Particles inan abrasive compact may have various shapes. Aspect ratio, the numericratio between the major and minor axes or diameter of a particle, may beused to quantify particle shape. An abrasive compact with a particleshape gradient may have a volume or region of the compact comprised ofparticles that have a spherical or blocky, shape that changes to a moreoblate, planar, whiskery shaped in another volume or region. An abrasivecompact may have a region with low aspect ratio particles that, througha continuous gradient, becomes a region with high aspect ratio particlessuch as platelets or whiskers. The higher aspect ratio regions may offerdifferent fracture, strength, or tribological, chemical, or electricalcharacteristics. In some embodiments, the maximum rate of change of theaspect ratio may be no more than 0.1 per one micron of translation (i.e.distance) along an axis.

In another embodiment, electrical conductivity and wear resistancegradients provide ultra-hard particle abrasive compacts for machiningmanufactured wood products. For these applications, a diamond basedabrasive compact with a high level of bulk electrical conductivity isdesirable to facilitate electronic spark machining of diamond cutters.Also for this application, high wear resistance is derived from astructure with a maximum content of coarse diamond particles. When suchcoarse diamond particles are incorporated in a monolithic, homogenousabrasive compact, electronic spark machining becomes more difficult.This embodiment solves this problem with coarse ultra-hard particles atactive cutting surfaces with a gradient to finer ultra-hard particlesand concomitant higher electrical conductivity. The continuous uniformgradient of particle size may provide a high bulk electricalconductivity with highly abrasion resistant wear surfaces.

Another embodiment applies the invented continuous gradients to othershapes. Annular abrasive compact geometries are suited to wire drawingdies. In these abrasive compacts structural or physical characteristicswill be varied to produce an annular surface with the desiredproperties. In annular shapes, some of the gradients will beapproximately perpendicular (radial) to tapered cylindrical or toroidalwear surfaces.

While compositional and ultra-hard particle size gradients have beendescribed, other gradients will have utility. Unimodal, multimodal, uni-and/or multi-axial gradients of potential use are: phase composition,particle shape, electrical conductivity, thermal conductivity orexpansion, acoustic and elastic properties, incorporation of other thanultra hard particle materials, density, porosity size and shape,strength, fracture toughness, optical properties.

In an embodiment, a method of creating an abrasive compact includesstarting with a group of ultra-hard particles, such as a preparedsynthetic diamonds, with a range of particle sizes. The particles arecombined and mixed with alcohol or another fluid to create a mixedslurry. The mixed slurry is allowed to segregate as influenced bygravity, centrifugal force, an electrical field, a magnetic field oranother method. The mixed slurry settles into a substantially solid,graded layer, optionally in which more of the coarse particles havefirst settled and more of the finest particles have settled last. Some,if not all, remaining liquid is removed by drying, centrifugation, oranother method. A portion of the graded layer is then removed andoptionally placed on a substrate. The layer of ultra-hard particles maybe oriented in order to place the surface having more coarse diamondparticles near the substrate to create an initial assembly, which isprocessed by sintering, typically under HPHT conditions, to create aprocessed assembly. From this processed assembly, a sintered diamondabrasive compact supported on a cobalt cemented tungsten substrate isproduced and recovered. The resulting supported sintered compact may befinished into an abrasive tool.

Optionally, the mixed slurry is allowed to separate in a non-planarfixture. An example of the non-planar elements of a fixture 2000 isshown in FIG. 20. As shown in FIG. 20, the fixture 2000 may include aplanar portion 2010 and non-planar portion 2020. The non-planar portionmay be of any non-planar shape, such as that of two ramps meeting at apeak, a conical shape, a hemispherical shape, a pyramidal shape, oranother non-planar shape. A larger concentration of coarse particles2030 will settle near the non-planar structure, while a largerconcentration of fine particles 2040 will settle at higher points awayfrom the non-planar structure. Also optionally, the carbide or othersubstrate may have an interface surface size and shape matching the sizeand shape of the settled diamond layer against which it is placed.

EXAMPLE Example 1 Prior Art

Following the procedures of U.S. Pat. Nos. 3,831,428; 3,745,623; and4,311,490. MBM® grade, 3 micron diameter synthetic diamond from DiamondInnovations, Inc. was placed in a 16 millimeter (mm) diameter highpurity tantalum foil cup to a uniform depth of approximately 1.5 mm. Ontop of this fine layer a second 1.5 mm uniformly thick layer of 40micron MBM powder was added. A 16 mm cylindrical 13 weight-percent (wt%) cobalt cemented tungsten carbide substrate was also placed into thetantalum foil cup. This assembly was processed following the cellstructure and teachings of cited patents at a pressure of 55-65 Kbar atabout 1500° C. for about 15-45 minutes. The recovered supported abrasivecompact had a sintered diamond layer structure supported on the cementedcarbide substrate. The structure of this cutter is shown in FIGS. 1 and2.

Example 2 Prior Art

A drilling cutter may be boiled in 3HCl:1HNO3 acid using methods such asthose described in U.S. Pat. No. 4,224,380 with its carbide substratecovered by a protective layer to yield a cobalt depleted region. Thestructure such a cutter is shown in FIGS. 2 and 3.

Example 3

45 grams of synthetic diamond with a particle size distribution shown inFIG. 17 may be prepared and combined with 450 cc of 99.9% pure isopropylalcohol. These materials may be mixed in a TURBULA® mixer for 2 minutes.The mixed slurry may be poured into a 100 mm diameter plastic containerand allowed to settle for 8 hours. The remaining liquid may be carefullyremoved by decanting and evaporation. Once the settled diamond layer issolid, a 16 mm disc may be cut out of the settled layer. The diamondlayer may be oriented in a tantalum (Ta) foil cup to place the coarseparticles near the tungsten carbide substrate. A cylindrical cobaltcemented tungsten carbide substrate may be placed on top of the coarsediamond particles. This assembly may be processed using HPHT processingat a pressure of 55 to 65 Kbar at about 1500° C. for about 15 to 45minutes. The exact conditions depend on many variables, these areprovided as guidelines. The recovered assembly will produce a sintereddiamond abrasive compact supported on a cemented tungsten carbidesubstrate, which may be finished into an abrasive tool. A sample of sucha structure was cut axially in half and polished for structureevaluation, the structure of this example is shown in FIG. 6.

To demonstrate the utility of this example's uniaxial continuouslygraded structure, several cutters were prepared and tested for impactand abrasion resistance. These results were compared to DiamondInnovations, Inc. TITAN commercial drilling cutters. Impact testing wasperformed on an INSTRON 9250 drop tester. Abrasion resistance(volumetric efficiency or G-ratio) was measured by turning a granitecylinder with a sharp, unchamfered cutter. The cutter of this exampleoutperformed commercial abrasion cutters by over 100% in impactperformance and 500% in abrasion. Detailed test results are shown inTable 1.

TABLE 1 Graded cutter Commercial cutter Average Abrasion G-Ratio 85 15(10{circumflex over ( )}5) Average diamond table 6.3% 13.0% Impactdamage after 10 drops at 20 J

Example 4

45 grams of synthetic diamond powder with the particle sizedistributions shown in FIG. 19 were combined with 12 grams of (99%purity and source) tungsten powder with the particle size distributionshown in FIG. 19 as in Example 3. The fabrication and sinteringprocesses were according to those of Example 3. The recovered compositecompact had a sintered diamond layer structure supported on the cementedcarbide substrate and could be finished for an abrasive tool. Onesintered tool was cut and polished for structure evaluation. Themicrostructure of this example is shown in FIG. 8.

Example 5

The settled diamond layer process of Example 3 was duplicated with theexception that the slurry was allowed to separate in a non-planarfixture as shown in FIG. 20 for 8 hours. As shown in FIG. 20, coarseparticles 2030 settled primarily near the non-planar structure, whilefine particles 2040 primarily separated above the non-planar structure.The drying and assembly process of Example 3 was performed except that acylindrical cobalt cemented tungsten carbide substrate 2050 with aninterface surface matching the size and shape of an interface surface ofthe settled diamond layer surface was placed on top of the diamondparticles. Sintering of Example 3 was duplicated. The recoveredcomposite compact had a sintered diamond layer structure supported onthe cemented carbide substrate and could be finished for an abrasivetool. One sintered tool was cut and polished for structure evaluation.The microstructure of this example is shown in FIG. 12.

The examples described above are not limiting. While sedimentation isdescribed, other methods may be employed, such as centrifugation,percolation, vibration, magnetic, electrostatic, electrophoretic,vacuum, and other methods. It will be appreciated that various of theabove-disclosed and other features and functions, or alternativesthereof, may be desirably combined into many other different systems orapplications. Also, various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art which are also intended tobe encompassed by the following claims.

1. An abrasive compact comprising: a plurality of superabrasiveparticles consolidated into a solid mass, the particles having acharacteristic gradient that is continuous, monotonic and uniaxial. 2.The abrasive compact of claim 1 wherein the characteristic gradientcomprises a particle size gradient.
 3. The compact of claim 2 in which amaximum rate of change of particle size is less than 1 micron ofparticle size per 1 micron of translation.
 4. The abrasive compact ofclaim 1, wherein the characteristic gradient comprises a pore sizegradient.
 5. The compact of claim 4 in which a maximum rate of change ofpore size is less than 1 micron of diameter per 1 micron of translation.6. The abrasive compact of claim 1, wherein the characteristic gradientcomprises a particle shape gradient.
 7. The compact of claim 6 in whicha maximum rate of change of particle aspect ratio is less than 0.1 per 1micron of translation.
 8. The abrasive compact of claim 1, wherein thecharacteristic gradient comprises a concentration of the superabrasiveparticles.
 9. An abrasive compact comprising: a plurality ofsuperabrasive particles consolidated into a solid mass, the mass havinga first continuous gradient along a first axis of the mass and a secondcontinuous gradient along a second axis of the mass.
 10. The compact ofclaim 9, wherein each of the gradients comprises a particle sizegradient.
 11. The compact of claim 9, wherein the first continuousgradient comprises a particle size gradient and the second continuousgradient comprises one of a pore size gradient, a particle shapegradient, or a superabrasive particle concentration gradient.
 12. Thecompact of claim 11, wherein the first continuous gradient is monotonicand uniaxial.
 13. The compact of claim 11, wherein the first continuousgradient is oscillating.
 14. A method of creating an abrasive compact,comprising: combining ultra-hard particles with a fluid to create amixed slurry; allowing the mixed slurry to separate and form a gradedlayer; removing remaining liquid from the graded layer; selecting aportion of the graded layer; placing a substrate against the selectedportion of the graded layer to create an initial assembly; processingthe initial assembly to produce a sintered abrasive compact supported onthe substrate to form a recovered assembly; and finishing the supportedsintered compact into an abrasive tool.
 15. The method of claim 14:wherein the allowing comprises allowing the mixed slurry to settle in anon-planar fixture; and wherein the placing comprises placing aninterface surface of the substrate so that the interface surface matchesa surface of the graded layer.
 16. The method of claim 14, wherein theplacing comprises orienting the graded layer and the substrate so that asurface of the substrate having more coarse particles is near thesubstrate.